Conventional rapid pyrolysis (RP) of biomass is a thermal treatment process in the absence of air, which produces char, liquid, and gaseous products [1-14]. In these processes, the pyrolysis temperatures range from 450° C.-600° C. and vapor residence times are less than one second to five seconds. In the RP process, liquid production is maximized at the expense of gaseous and solid products. The liquid product (bio-oil or biocrude) is generally unstable, acidic, corrosive, viscous, and has high moisture content [15-18]. The poor stability of biocrude oils is attributed to the char and alkali metals in the oil, which catalyze secondary reactions during storage [17]. However, if the hot pyrolysis vapors are filtered to reduce the char content before condensation, the stability of the oil is improved considerably [18].
Biocrude oils are complex mixtures of carbohydrate and lignin thermal decomposition products, which cannot be used for most biobased products and fuel applications except after considerable secondary processing. Secondary processing such as catalytic upgrading [19-26], liquid-liquid extraction [27-29], or gasification [30-35] increase the cost of the final product and make it less economically competitive relative to fossil derived products.
Catalytic studies of biomass pyrolysis products have focused on upgrading of pyrolysis oils (post pyrolysis catalysis) to higher value products [19-26], but most of these studies reported low yields of hydrocarbons, high coke/char yields, and rapid deactivation of the catalysts. Other catalytic studies of whole biomass feedstocks focused on gasification to synthesis gas [30-35], but fractional pyrolysis has not been reported in published literature.
Biomass feedstocks are composed of structural (lignin, cellulose, and hemicellulose) and non-structural (extractives) components, which have distinct chemical properties. It is conceivable to selectively convert the biomass constituents to a defined slate of chemicals and separate these products in situ (fractional pyrolysis) without necessarily going through secondary extraction and upgrading processes. Fractional pyrolysis is defined as a selective in situ conversion of biopolymers to desired products. This approach is aided by catalysts and can produce a narrow slate of pyrolysis products, which can be tailored to specific applications. This approach has potential application for converting whole biomass feedstocks, biomass-to-ethanol residues, and organosolv lignins (pulping residues) into high-value products. Potential products include synthesis gas, phenol formaldehyde resins, phosphate esters, magnetic wire, cleaning and disinfectant compounds, ore floatation, and miscellaneous applications.
As such, there remains a need in the art for processes to selectively convert biomass components in situ into suitable, stable products using suitable catalysts and thus eliminating potential secondary processing steps.